It has been known prior to the present invention to displace crude oil from petroleum-bearing formations through the use of solvent floods which, under the appropriate pressures, will form liquid or liquid-like fronts more or less similar to the aqueous flooding media or displacing fluids which have become far more common in practice. The solvent-type flooding media or displacing fluids used in the past have generally been light hydrocarbons, ranging from ethane to pentane, and sometimes including hydrocarbons up to about 9 carbons in length, compressed to a density high enough that they are miscible with and/or act as solvents for many of the lighter components of the petroleum in the porous oil-bearing formations. The injected flooding media together with the lighter hydrocarbon fractions of the crude oil with which they are miscible tend to combine to displace the heavier fractions from the oil-bearing pores of the formation, as proposed by Hutchinson and Braun in "Phase Relations of Miscible Diosplacement in Porous Media", Am. Inst. of Chem. Engrs&gt;Jnl., v 7 (1961) pp 64-74.
Light hydrocarbon flooding has been used commercially as a practical method of displacing crude, but has not been as widely accepted as waterflooding at least partly because of the great difference in viscosities of the flooding media from that of the crude oil; light hydrocarbon flooding media tend to flow freely in the more permeable portions of the formation, bypassing the less accessible and more viscous crude oil in the greatest part of the formation. As is known in the art of crude oil displacement, the escape or dissipation of the injected fluid in this manner is highly inefficient and has long been a problem for those interested in devising ways to displace crude oil from oil-bearing formations. We are not aware of any successful attempts to introduce polymers or other viscosity-modifying materials to light hydrocarbon displacing media to control their mobility in the formations.
The formation of coordination polymers by certain organotin compounds under certain conditions was described by Janssen, Luijten and van der Kerk in 82 RECUEIL 90 (1963) and 1 J. Organometallic Chemistry 286 (1964). Tributyltin fluoride was shown to be a coordination polymer in solution by Dunn and Oldfield, J. Macromolecular Science A4(5) pp 1160-1176 (1970). Solutions of tri-n-butyl tin fluoride in hexane were described as having very high viscosities which may be significantly reduced by the addition of polar solvents to the solutions.
The following explanation has been offered in the literature for this behavior of organotin fluoride compounds in solution. A single isolated molecule of, for example, tri-n-butyl tin fluoride possesses a dipole moment due to the electronegativity difference between tin and fluorine. This leads to a weak dipole-dipole type interaction between adjacent molecules, resulting in tin atoms becoming pentacoordinated and linked through fluorine bridges. As all the organotin fluoride molecules possess this dipole moment, an infinitely long yet transient linear polymer chain is formed. These transient chains cause a large increase in viscosity of the solution, and yet are not subject to permanent damage, as are ordinary polymers, due to excessive shear strain in the solution.
Relevant patent literature includes U.S. Pat. No. 3,979,354 to Dyckman et al, wherein trialkyltin groups are incorporated in various kinds of polymers and utilized for their antifouling abilities. The trialkyltin moieties do not form polymers themselves in this disclosure.
Example VI of U.S. Pat. No. 4,086,297 illustrates the addition of tributyl tin fluoride in high concentrations to thermoplastic film-forming polymers to render them microbiocidal. No inference is raised, however, of the formation of a TBTF polymer at any stage of the process.
In U.S. Pat. Nos. 4,153,574 and 4,191,580, Beiter and Hafner state that tributyl tin fluoride has a "strong tendency to agglomerate" when dispersed. The "unusual behavior" is explained in column 1, lines 32-38, i.e. a relatively weak attractive force on the tin atom of one molecule and the fluorine atom of another results in a structure resembling a linear polymer molecule. The undesired formation of this molecule is prevented through the use of various additives.
The delayed gelation of polymers and other materials in formation plugging and the like is reviewed in U.S. Pat. No. 4,461,352, which employs a borate salt with acrylamide polymers; the gel formation is pH and temperature dependent.
The reader may also be interested in the in situ formation of chromium-containing polymers for the stabilization of clay in subterranean environments disclosed by Kalfoglou in U.S. Pat. No. 4,129,183; aside from the differences in chemical structure of the polymers created and the different objectives of the inventors, the topical process of Kalfoglou is conducted in aqueous solution, which we do not employ.